(1) Field of the Invention
This invention pertains generally to fluid conditioning apparatus, and is more particularly concerned with air conditioning apparatus and systems such as employed, by way of example, in aircraft.
(2) Description of the Prior Art
The prior art of fluid conditioning systems is typified by several generally conventional approaches to the problems of elastic fluid conditioning, which usually provide for the removal of entrained moisture from the ambient air admitted to the air conditioning system of an occupied vehicle such as an aircraft. Such a typical system utilizes a source extracting air from the ambient atmosphere and compressing it for use, such as a jet engine or other compressing source onboard the aircraft. The compressed air may be passed in heat exchange with a heat sink, as for example ducted ambient air, to reduce its heat content, after which it may be subjected to additional energy extraction to accomplish pressure reduction and still further temperature drop, as for example by use of an expansion turbine.
If the source air contains any amount of moisture up to the point of admission to the turbine, condensation of a large portion of the water may occur in or immediately downstream of the turbine, and steps to extract or separate the condensed water from the entraining stream are essential. In the usual case, the air at this stage is a relatively low pressure and the separator component comprises a water separator enclosing a coalescer bag to coalesce the water (which is in mist or fine droplet form) into relatively larger droplets. The separated water then drains off the bag and is removed from the separator component by means well known in the art.
Since the water separation takes place in the low pressure sector of the system, the marginal element is the water separator per se because it has been discovered that this component is extremely susceptible to the operating environment. That is, an unfavorable environment can escalate the servicing frequency of the coalescer bag to more than a nuisance value inasmuch as the required dense bags become easily contaminated. Attempts to alleviate this problem by exploring numerous paths of development of materials for coalescing the mist and droplets have been uniformly unsuccessful.
It was then considered that removal of the moisture upstream of the expansion turbine, or other expanders, in the zone of higher pressure, could be accomplished with condensing means other than coalescer bags by utilizing the low temperature discharge air of the turbine to cool the turbine inlet air to the desired level in a condenser heat exchanger. By this means a significant percentage amount of the entrained moisture could be condensed at a relatively warm temperature. However, in the past the major drawback to the high pressure water separation has been that the reduction in turbine inlet temperature to achieve the desired condensation has resulted in a loss of turbine power with a resulting loss of cycle efficiency and performance. Attempts to overcome this problem of loss in performance have resulted in complications such as condensor bypass circuits and the like.
With this background in mind it was further conceived that the relatively simple addition of a reheater heat exchanger upstream of the expander would be a major step forward to the problem solution, as was proven by a design study followed by actual reduction to practice in a development embodiment.